By the term "implants" is understood artificial organ parts, which assume their functions or partial functions temporarily or permanently in human or animal bodies. Joint replacement parts, skeleton replacement parts, tumor prosthetics, tooth replacements, such as implantable teeth, or similar parts of the human or animal body, are involved.
Known implantations of the above-mentioned type are composed in many cases, completely or partially, of metal, particularly high-duty or refined steel. It is, however, also possible to use in particular the following materials: glass ceramic, sintered ceramic, osteoceram materials, various types of glass (particularly in the form of coatings for metal), alone or worked together, for the construction of implants.
It is known that with metal implants particularly the disadvantage of insufficient corrosion and stress corrosion resistance of the metal against the fluids and secretions of the living body, as well as the insufficient abrasion resistance with implant parts conducted relative to one another, are problems which arise in use. Metallic particles possess the danger that they will be led into the surrounding tissue and imbed themselves there, which can lead to very serious injuries, such as for example the appearance or manifestation of irritations, and stiffening of joints, and which decrease the service life of the implants.
For these reasons, metallic implants have been developed which are coated completely or partially with enamel. Such implants are described, for example, in German Offenlegungsschrift No. 23 40 546. Correspondingly, particular embodiments of such implants can possess a coating of partially crystallized enamel, and they can also be provided with multi-layered application of enamel, whereby if necessary, a partially crystallized base enamel can be located on the base metal. With such a multi-layered application of enamel it is advantageous to provide a glassy covering enamel. In each case it is preferred that the enamel surface be locally profiled, for example by mechanical or chemical roughening or by means of engraving of indentations.
It has, however, turned out that the connection between implant and the tissue which surrounds the implant after placing it in the body of the human or animal patient, is still in need of improvement. Therewith it is to be considered that the connection between implant and tissue should exclude relative movements within limit ranges. This connection is, in addition, to be so provided that the biophysical control system of the tissue, injured or broken as a result of the operation, be reinstated or restored as much as possible to its specific impulse patterns, which in all cases represent regulating stimuli for growth and maintenance of the tissue, by means of material-determined connection. Therewith it is moreover to be considered, that through construction and chemical state of the surface, occurring mechanical forces be distributed and transferred in optimal manner to the bones. Although also different bioelectrical and biochemical characteristics (e.g. piezoelectric city and surface groupings of bone collagens and current potential in the osteone system) intervene, which according to previous knowledge contribute to variations in bone material, these should be as well compensated or maintained as possible with implants.